A framework for the synthesis of multiphase reacting systems
A framework for synthesis, development, and design of reactors for multiphase reacting systems is presented. The reactor development begins in the laboratory, where the reaction is tested in micro- or bench scale reactors to identify systems which hold a potential for commercialization. The proposed systematic methods guide the user to consider key issues and phenomena that have to be considered at various scales, and the tools that can be invoked to tackle them.
For gas-liquid catalytic and non-catalytic reactions, the first step involves screening of various reactor types for the reaction under consideration, and identification of alternative designs as candidates for further studies. Special emphasis is placed on situations where there is a great deal of uncertainty regarding reaction kinetics, and little is known about potential limitations in heat and mass transfer. This procedure is then extended to tackle multiple reactions involving heat effects. Multiple reaction schemes are discussed, with the objective of maximizing the yield or selectivity of a desired product. The results of the screening procedure are used to propose a multiphase reactor network superstructure. Nonlinear programming is used to identify the optimum subset of the above superstructure for a specified reaction scheme and objective function.
Further reactor screening and development is illustrated for two- and three-phase fluidized bed catalytic reactors. A family of reactor models appropriate for particular reactor types and flow regimes is used to further tighten the performance estimates of the candidate reactors proposed in the earlier steps. Additionally, scale-up criteria are proposed to directly scale up the bench scale reactors to the commercial scale, while maintaining a similarity in some reactor performance index such as the conversion, the product yield or selectivity.
A similar approach is applied to the design of reactive crystallization and precipitation systems. The conventional equilibrium based design procedures are extended to incorporate the effects of mass transfer, and the kinetics of reaction, nucleation and crystal growth, by proposing a new, generic model. The reaction, mass transfer and dissolution Damkohler numbers, and the nucleation and growth numbers which result from the generic model, represent the relative rates of the individual steps, and their effect on the process paths, the resulting crystal size distribution and the crystallizer productivity is discussed for systems involving up to four components.